1. Field of the Invention
The invention relates to a system and method for measuring the thickness of a zinc layer on steel and/or for measuring the iron content and iron concentration, respectively on a zinc layer. Further thereto to the invention relates to the use of a dispersive ionization chamber for material testing.
2. Description of the Related Art
Steel sheets are galvanized in order to make them more corrosion-resistant. The determination of the thickness of the zinc layer is essential in order to ensure on the one hand a predetermined minimum thickness of the zinc layer for guaranteeing the corrosion—resistance and on the other hand for the purposes of economizing resources that no too thick zinc layers are applied.
EP 0 465 797 B1 discloses an apparatus for measuring the iron content in zinc layers and/or for measuring the thickness of a zinc layer by x-ray fluorescence. The apparatus disclosed therein has the disadvantage that a zinc application of maximum of 350 g/m2 can be determined. A higher zinc application cannot be measured by such apparatus.
Particularly for manufacturing crash barriers and for manufacturing trucks it is desired to apply a zinc application of more than 350 g/m2 on a steel sheet. Further, it is desired that in strip zinc coating lines a verification system is implemented which can determine a zinc application over a larger measurement range.
During steel manufacturing a strip like steel is coated with zinc for increasing resistance against corrosion. Thereafter, a so called galvannealing process may be performed. Thereby, galvanized steel is subsequently heated to approximately 500° C. to approximately 600° C. By such galvannealing iron diffuses into the zinc layer such that inter metal compositions and an inter metal alloy between zinc and iron is generated. This inter metal composition is of major importance for further processing of the coated steel and for the adherence properties of the zinc layer. Hereby, it is essential that during the manufacturing method the iron ratio in the zinc layer is adjusted within the narrow bounds in order that the method is performed reproducible. Accordingly, it is important, that the iron content in a zinc layer is verified in a non-destructive manner.